1. Field of the Invention
This invention relates to steelmaking, and more particularly to a versatile steelmaking method and apparatus having both electric-arc furnace and basic-oxygen furnace capabilities.
2. Description of the Prior Art
The face of the steelmaking industry in the United States and throughout the world has changed considerably in the past 20 years due to widespread acceptance of the basic-oxygen process. In that steelmaking process a charge of steel scrap, molten iron, and slag-making additives in an open top metallurgical vessel is refined into steel by means of a high velocity stream of high purity oxygen issuing at near supersonic velocity from a lance extending into the vessel in a manner whereby oxygen passes downwardly and into the molten charge. The process now enjoys a greater annual tonnage production than basic open hearth steelmaking, long the mainstay of the industry. With the basic-oxygen process it is possible to prepare 200 tons or more of steel in as little as 30 minutes. By way of comparison, the basic open hearth process would consume at least several hours to prepare the same tonnage of steel.
In addition to the basic-oxygen process, the electric-arc process of manufacturing steel is likewise seeing ever increasing usage in the steel industry. In the electric-arc process, a solid charge, typically steel scrap, is placed in an open top metallurgical vessel having a rather broad dish-shape character. An electrode-bearing roof is placed upon the open top vessel to form an electric-arc furnace. The charge is then melted into usable steel by means of electrically generated heat in the electrodes. The electric-arc steelmaking process has certain advantages over the basic-oxygen steelmaking process. Chiefly, the electric-arc process utilizes a high percentage of steel scrap in the furnace charge. In fact, the charge may be substantially 100% steel scrap. The basic-oxygen process cannot ordinarily accept more than about 30% by weight solid scrap in the furnace charge, unless special measures are used. This limitation is due to the fact that the basic-oxygen process derives most of the heat required for refining by exothermic chemical reactions of the oxygen blown into the vessel with oxidizable impurities in the charge, chiefly carbon and silicon. Additionally, the basic-oxygen process has not been successfully used to make many grades of alloy and special steels for which it appears to be unsuitable. Both basic-oxygen and electric-arc steelmaking are batch processes and have the disadvantages of a batch-type operation.
This invention provides a versatile steelmaking process and apparatus therefor which has both basic-oxygen furnace and electric-arc furnace capabilities. The method and apparatus of the invention have the advantages of each of the foregoing processes and substantially overcome their respective disadvantages. In addition, the method of the invention may provide a continuous or semi-continuous steel-making practice by which almost any desired grade of steel may be manufactured. The method of the invention provides combined electric-arc furnace and basic-oxygen furnace steelmaking, and are versatile such that ordinary basic-oxygen furnace steel-making practices may be employed within the method where desired. Moreover, the invention provides novel steelmaking practices and steelmaking plant designs whereby steel of varying quality and compositions may be produced in a rapid and economical fashion.